Corrosion retarder



Patented Jan. 11, 1049 CORROSION BETARDER John T. Ruclrer, Lewlston, N.Y., assignor to Hooker Electrochemical Company,

Nia ara Falls, N. Y., a corporation of New York No Drawing. ApplicationSeptember 27, 1946,

' Serial No. 699,840

3 Claims.

My invention relates more particularly to retarders of corrosion ofmetals by acids.

It is known that certain substances exert 'a protective effect uponmetals, against attack of acids thereon, by rendering the metal passivewith respect to the acid, i. e., as anti-catalysts. I will refer tothese hereinafter as inhibitors. It is also known that certain othersubstances exert a protective effect by interposing a fllm between themetal and the acid. These are of the nature of detergents, or dispersingor wetting agents, characterized by low surface tension. I will refer tothese hereinafter as "surface active materials.

Among the agents of the inhibitor category are the aralkylthio-cyanates, such as benzyl and cymene thiocyanates. These are typical'examples of aralkyl thio-cyanates, each 'having a methyl group, towhich the thio-cyanate group is attached, and the cymene having, inaddition, a propyl group. However, these compounds are of low solubilityin acid pickling baths. Also, benzyl thio-cyanate has not only anexceedingly disagreeable odor, but toxic and lachrymatory properties,the efiects of which are aggravated by its low solubility and consequenttendency to collect at the surface of the bath and spatter into theatmosphere. For these reasons, these compounds have heretofore hadlittle importance, except under conditions permitting of vigorousagitation.

Among the agents of the surface active category are the quaternaryammonium compounds, such as lauryl pyridinium chloride and lauryldimethyl benzyl ammonium chloride. These are selected examples ofquaternary ammonium compounds in which the nitrogen is in the ring and.

Example I Metal, steel Acid, sulphuric. 25% Temperature, 20 C. Corrosionretardcr... None LPG LPG LDBAC LDBAC Per cent retarder by m. p.hr.,g.0034 .0000057 .00019 .00011 .00018 Protection, percent 99.84 94.4 96.794.5

Example II Metal steel Acid, hydrochloric 20% Temperature, 20

Corrosion retarder... LPC LDBAC LDBAC LPG None

Per cent retarder by 1 p. hr., g 0043 Protection, per cent Example IIIrespectively LDBAC LDBAC LPC LPC

. None Example IV Metal, steel Acid, sulphuric 15% Temperature, C.

Corrosion retarder Per cent retarder by wt Wt. Loss per sq. c. m. p.hr., 2.. Protection, per cent Lauryl pyridinium chloride and lauryldimethyl benzyl ammonium chloride are partically odorless. They arewater soluble and also quite soluble in oils. I have now found that,when these compounds are used in combination with benzyl or cymenethio-cyanates they act as dispersing agents for the thio-cyanates,besides increasing their solubility. Moreover, the foam layer formed bythe surface active agents suppresses the tendency of the thio-cyanate tospatter and renders its use unobjectionable. In substantially equalproportions by weight lauryl pyridinium chloride forms with benzylthiocyanate a eutectic melting at 15 C. In the same proportions it formswith cymene thio-cyanate a composition that is liquid at roomtemperature. I have found these compositions to be exceptional corrosionretarders.

This is illustrated by the following example:

Example V Metal, steel Acid, sulphuric, 15%

Temperature, 75 C.

Corrosion retarder LDBAC 50% LPC 510% LPC 50% B'IC 50% CIC 50% BTC 50%Per cent retarder by wt .02 .02 .02 Wt. loss per sq. c. m. p. lir., g..0011 .001 .00076 l rotection, per cent 99.1 99.2 99.4

It will be seen by comparison of Example with Examples III and IV thatthese compositions are extremely effective. They are not in every casemore efiective than thio-cyanate by itself. but itmust be rememberedthat these compositions are entirely practicable, whereas thethiocyanates are generally impracticable. However, the LPC-BTC eutecticis more efiective than either of its constituents.

When added to acid pickling baths, these corrosion retarders have ingeneral a selective protective effect upon the metal, as compared withits oxide. This is illustrated by the following:

Example VI Mew], steel, hezlvilv coated with brown rust Acid, sulphuric.15% Temperature, 75 C. Corrosion returdcr. None L PC 50% B'iO (WI, Percont rctarder 0. 1 Time of cleaning, minutes Ii. ti

Example VII Metal, steel heavilv coated with blue scale Acid, sulphuric,15% 'icmneruturc. 75 C. Corrosion retarrlcr None LlC 50% BIC 50% Percent retardorn 0 Tim: of cleaning, minutes 0.5 0.7

It will be seen from Examples VI and VII that the addition of arelatively large quantity of one of my preferred corrosion retarders tothe pickling bath increased the time of pickling only very slightly,

In order to show that my corrosion retarders have exceptionalproperties, I present herewith a table showing the percentage ofprotection afforded to ferrous metals by a considerable number of thebest known corrosion retarders, against 4 per cent sulphuric acid at 71C. This table is taken from Chemical Industries, 1935, vol. 37, page124. The first part of this table is a comparison of certain retarderson the-basis of an equal percentage by weight. The second part is acomparison of certain other retarders on the basis of an equal molecularpercentage. To each part I have added lauryl pyridinium chloride, laurylpyridinium thio-cyanate and my LPC-CTC and LPC-BTC compositions, on theappropriate basis.

Mols Per Wt. Per Protection Remrder Liter Cent Per Cent Sulionated oiL.,0.1 Nitrogen base oil. 0. 1 30 Paper waste liquor. 0. 1 1:3 Sulfonatedanimal mattcL 0.1 63 Low grade wheat flour 0. l 85 Nitrogen bases. 0.188 Cool 'lnr nitrogen hoses 0.1 05 Lnuryl pyridinium LhlOl 0. 1 85 LPG-TC .l 0.1 90.4

LPC BlC eutectic l 0. l 0!). 00 Trietliylamine .01 10.5 Aniiine .01 .0914.5 Pyridine 01 .08 19.0 Quinoiine 01 .13 49,4 Acridine .01 .18 82.4 2me-quinolme l 01 .15 53. 0 xnc-ncridine 01 81. 8 Phenyl acridinc 01 .2990. 2 Dimrthyl-diethyl-d[amino ucridino hydrochloride... .01 .33 09, 8Lauryl pyridinium chlorid .01 .20 81. 8 LPC-CTC l 01 99. 5 LIC-B'ICeutectic .01 .22 09. 99+

It will be seen from the above that lauryl pyridinium chloride andlauryl pyridinium thiocyanate rank high among corrosion retarders, andwhen it is remembered that they have the advantage over most of them ofhigh water solubility and freedom from offensive odor their importanceas corrosion retarders will be manifest. It will also be seen that myLPCBTC eutectic tops all of 'the list, since in equal weight ormolecular proportion it has a higher protective value, and for a givenprotective value much less of it need be used. It should be noted thatwhile the difference between protective values of 99.8 and 99.99+ is notmathematically great, itssignificance is enormously important, for itmeans that in the latter case the corrosion rate is less than onetwentieth. In other words, steel subjected to 4 per cent sulphuric acidat 71 C. will last more than twenty-times as lon if protected by myeutectic as if protected by the best of the previously known corrosionretarders.

Corrosion retarders are useful wherever acids are handled in metalequipment, of which pickling of metal is only one of many illustrations,acid treatment of oil wells being another, Another use for suchretarders is in lubricants, which are liable to develop acidity throughoxidation, by contact with the air. Organic acids developed inlubricating oils, such as those used in automotive crank cases, are mildcompared with pickling acids, but the time factor is measured in monthsinstead of hours, and in the long run the corrosive effect of such acidsmay be very serious, especially upon bearing alloys, such as thosecomposed of lead, tin. copper and less commonmetals. It is difilcult togive a quantitative measure of the eifect of corrosion retarders inlubricating oils, as the matter is complicated by wear. Nevertheless,visual comparison of the effects of lubricating oils upon bearings, withand Without my retarders, indicates that my retarders have a usefulefiect in such oils.

While I have given examples of the results obtained with my compositionsonly in equal proportions by weight, I do not wish to be limited to suchproportions, as.any small addition, such as 10 per cent, of these andother analogous aralkyl thio-cyanates, of low solubility, to thequaternary ammonium compounds mentioned and other analogous compounds,of good solubility and having the property of dispersing, and increasingthe solubility of, the thio-cyanate, will improve the corrosionretarding properties of the quaternary ammonium compounds, and theaddition of as little as 20 per cent of the latter to the thio-cyana-teis useful in suppressing its spattering tendency. Also, while in theexamples the proportion of corrosion retarder ranges from 0.02 to 0.1per cent by weight, I do not wish to be held to these limits, as myretarders are useful in proportions as low as .005 per cent, and thereis no objection to using up to 5 per cent of the retarder.

In the foregoing examples I have given tests only of compositions ofbenzyl and cymene thiocyanates with lauryl pyridinium chloride andlauryl dimethyl benzyl ammonium chloride, but these are given as typicalonly. Besides these, many combinations of other aralkyl thio-cyanates,such as xylyl thio-cyanate, and mesityl thio-cyanate, etc., with otherquaternary ammonium compounds, such as lauryl pyridinium sulphonate,trimethyl cetyl ammonium chloride, amido benzyl pyridinium chloride,etc., form compositions which are superior retarders of corrosion ofmetals by acids. In short, any aralkyl thiocyanate in combination with aquaternary ammonium compound, and in particular those having an acidradical and an a kyl group of at least 10 carbon atoms attached to thenitrogen atom, the remaining nitrogen valences being satisfied by carbonmembers of one or more hydrocarbon rad- 1. As a new composition ofmatter, useful as a' retarder of corrosion of metals by acids, asubstantially eutectic mixture consisting of lauryl pyridinium chlorideand benzyl thiocyanate in substantiall equal proportions by weight.

2. The method of eliminating at least 99.99 per cent of the corrosion offerrous metals by be benzyl and the others I acid pickling baths, suchas 4 per cent sulphuric acid at 71 0., which comprises incorporating inthe acid substantially 0.1 per cent of its weight of a substantiallyeutectic mixture consisting of lauryl pyridinium chloride and benzylthiocyanate.

3. The method of protecting bearing metals in automobile crankcasesveioped in lubricatingoils during use therein, which comprisesincorporating in the oil 0.005 to 0.1 per cent of a substantiallyeutectic mixture of lauryl pyridinium chloride and benzyl thiocyanate.

JOHN T. RUCKER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED s'ra'ms PATENTS 15 Number 1 Name Date 2,006,218 MacArthur et a1.June 25, 1935 2,016,035 Downing et al Oct. 1, 1935 2,203,849 FelkersJune 4, 1940 2,298,483 Frey et a1. Sept. 22, 1942 against organic acidsde- I

